With the continually diminishing size of electronic devices, the heat generated by such devices can cause structural damage due to over-heating. It is highly desirable to design and fabricate thermal interface materials (TIMs) with exceptionally high thermal conductivity for transporting heat efficiently from electronic components to a heat sink.
One such thermal interface material is a carbon nanotube (CNT), which has shown unique and attractive mechanical, electrical, and thermal properties. Several studies have revealed that CNTs have unusually high thermal conductivity in their axial direction. For example, molecular dynamic simulations of a single-walled nanotube (SWCNT) indicated that the thermal conductivity of the SWCNT can be as high as 6600 Wm−1K−1 at room temperature. See “Unusually High Thermal Conductivity Of Carbon Nanotubes” by Berber et al. “Thermal Transport Measurements of Individual Multiwalled Nanotubes”, Kim et al., Phys Rev. Lett., 87, 215502-1, 2001 disclosed measuring the thermal conductivity of a single multi-walled carbon nanotube (MWCNT) using a micro-fabricated suspended device, and their measurement showed that the thermal conductivity was larger than 3000 Wm−1K−1 at room temperature. Realizing that CNTs are good TIM candidates, efforts have been made on the use of dispersed CNTs as thermal conducting fillers in polymer composites. For example, “Thermal Conductivity Improvement of Silicone Elastomer with Carbon Nanotube Loading,” Liu et al., Appl Phys Lett., 84, 4248, 2004 reported a thermal conductivity ranging from 1.1 to 1.9 Wm−1K−1 as the CNT loading in a polymer composite increased from nil to 3.8 wt %. The below-expectation enhancement could be attributed to the random orientation of CNTs in the polymer matrix and the existence of interface thermal resistances between the actual heat source/sink and the TIM device. To avoid these problems, Huang et al. disclosed in “Aligned Carbon Nanotube Composite Films for Thermal Management” Adv. Mater., 17, 1652, 2005 growing aligned CNTs on a silicon substrate and then fabricated a polymer composite film with such protruded, aligned CNTs running from one side of the TIM device to the other. An enhancement in thermal conductivity from 0.56 Wm−1K−1 for the pure elastomer matrix to 1.21 Wm−1K−1 for the same polymer embedded with a 0.4 vol % aligned CNT array was obtained. Despite the fact that aligned CNTs should have formed ideal thermal conducting paths through the composite structure, this enhancement was still far below expectation.
Various techniques have been developed for growth of aligned CNTs in well-aligned configurations, including plasma or laser enhanced chemical vapor deposition (hereinafter referred to as “CVD”) process by Vander et al., J. Phys. Chem. B., 106, 13122, 2002, hydrocarbon-ferrocene/ferric carbonyl mixture by Srivastava et al., Carbon, 39, 201, 2001 and also by Lee et al., Appl Phys Lett., 82, 448, 2003 and CVD of hydrocarbon on metal thin films by Ant et al., Appl Phys Lett., 81, 3464, 2002 and also by Merchan et al., Carbon, 42, 599; 2004 or pattern printing catalysts by Lee et al., Letters to the Editor/Carbon, 42, 667, 2004 on substrates.
There remains a need for a method of synthesizing an aligned carbon nanotube multilayer composite on both sides of a metallic substrate.